Modern electronic systems often employ a number of electronic circuit modules, typically printed wiring boards (PWBs) or printed circuit (PC) cards populated with electronic components and connectors, mounted in an electronic housing or rack. Typical racks often include a plurality of card slots for receiving circuit modules, with card edge guides to hold the cards in alignment, insertion/removal elements, a card connector, and a backplane for providing circuit interconnections. Circuit backplanes are often multilayer printed wiring boards designed for high speed interconnection of signals between different circuit components mounted on physically separated circuit modules in different slots. In most configurations, the circuit modules include electrical connectors affixed to the rear of the circuit module that are plug-action coupled to mating connectors on the backplane.
In some rack configurations, for example those employed in the cable television (CATV) and other telecommunications equipment industries, the circuit modules include discrete drop side signal connectors (electrical and/or optical) affixed to the circuit modules that couple to cables that carry signals to and from the equipment rack. In some of these configurations, the discrete signal connectors are mounted to the rear edge of the circuit modules and extend through openings in and the backplane and the housing rack so as to allow connection of the drop side signal cables. In other configurations, connectors are provided on the front edge of a circuit module to allow for signal insertion and extraction.
Most equipment users would prefer that signals be input and output from the back surface of a card rack, since excessive cabling on the front of a rack clutters the area around the equipment rack, as well as interferes with card insertion and removal. One particular exception to this preference is the provision of optical fiber connectors, which by preference in some industries are provided on the front of circuit boards for ease of cleaning and maintenance.
Circuit board housing racks in some applications are complicated by the need to accommodate different types of circuit modules that effect different types of signal processing. For example, the cable television (CATV) equipment industry has recently been expanding its service offerings to provide services beyond that of the traditional television service. For example, many cable television companies now provide telephone service, local and wide area network (LAN/WAN) data communications service, and Internet service. A modern CATV headend thus serves as a multi-type signal communication hub that allows various types of signals to be input, extracted, or passed through to other signal nodes in the CATV network. These expanded service offerings require handling, of many different types of signals, and insertion and extraction of the signals for communications over the coaxial and optical fiber cable plants.
Telecommunications equipment, especially CATV headend equipment, must now accommodate a wide variety of different types of electronic circuits to handle the adding, dropping, and passing of signals of various types, e.g. baseband video, IF modulated video, S-video, telephone signals, Internet (TCP/IP) traffic, 10 and 100 Base-T network traffic, etc. Prior to communication, these signals must be converted into a format suitable for carrying via the cable or fiber optic plant. Conversely, these signals must be extracted from the coaxial or optical fiber cable and converted into a suitable form for utilization, distribution, further processing, etc. There is therefore need, particularly in the CATV industry, for circuit module racks that can accommodate various circuits and input/out cabling for processing, input, and output of various signal types.
The need to accommodate the wide variety of signal types for input and output complicates the design of the circuit board rack. One approach to the problem of different signal types is the provision of one or more permanently mounted connectors on the back panel of the card rack for connection of the signal cables. This approach is used in the DV6000 digital video transmission system, manufactured by ADC Telecommunications, Inc.
The main problem with this approach is that a card slot becomes "dedicated" to a particular type of circuit module with the provision of a particular connector configuration permanently affixed to the rack back panel. Modern telecommunications equipment must be adaptable and flexible to rapidly changing needs and equipment design. It is not desirable to lock in a particular configuration of an expensive piece of equipment such as a card rack by permanently mounting connectors to the back of the rack.
Another approach to the multi-type signal problem is a circuit module that has a first connector that plugs into a socket in the backplane and has a second type of signal connector that protrudes through an opening in the backplane. Cabling for the card's input/out signals is connected directly to the protruding signal connector.
With this approach, extraction of a card for servicing or replacement in the event of failure becomes a three-step process: First, a technician must access the rear of the enclosure to disconnect the cable from the circuit module. Second, the technician then must return to the front of the enclosure to remove the card. The third step involves a return to the back of the rack to reconnect the cable after a new or repaired card is inserted. Often, the signal cable is left dangling or moved aside during servicing; if care is not taken to label the cable or tie it up in a safe place, confusion and servicing delay can result. The problem is exacerbated if multiple cards are extracted simultaneously, leaving multiple disconnected cables dangling.
Therefore, there is a need in certain electronics equipment configurations, especially those in the CATV equipment industry, for a circuit board rack that allows more ready insertion and extraction of a circuit board module for service, without requiring frequent access to the rear of the equipment rack. Furthermore, there is a need for circuit board rack wherein a particular slot can be connectorized for a particular type of circuit module with its particular types of electrical connectors and cabling, but can be reconfigured in the event of a change in the equipment or type of circuit board that needs to be accommodated in a particular slot.